FIG. 20 is an enlarged sectional view of a chief part of a conventional high pressure discharge lamp. A short arc extra-high pressure discharge lamp, as an example of the conventional high pressure discharge lamp (hereinafter, the conventional high pressure discharge lamp is referred to as a “high pressure discharge lamp 1”), has a light-emitting part 3 and a pair of sealing parts 4 extending from opposite sides of the light-emitting part 3. In the light-emitting part 3, a pair of electrodes 2 are arranged so as to oppose each other, and mercury having a density of 0.15 mg/mm3 or more is enclosed. The sealing parts 4 seal respective ends of the electrodes 2. The electrode 2 has a rough surface 6, and a small gap has been formed between the surface of the electrode 2 and the sealing part 4, which is made of a silica glass (e.g. see Patent Literature 1).
In a process of manufacturing the high pressure discharge lamp 1, by vibrating the sealing part 4 when the electrode 2 is sealed by the sealing part 4, a molten silica glass existing in a recessed portion 6a of the rough surface 6 of the electrode 2 is brought out of the recessed portion 6a, so that a gap is formed between the sealing part 4 and the electrode 2. The gap reduces stress concentration at an interface between the surface of the electrode 2 and the silica glass, thereby making the sealing part 4 less prone to breakage. A surface of the electrode 2 has been roughened only to form the gap, and therefore a surface of the electrode 2 only need to have a recessed portion 6a. 